1. Either use a reserve die or pull a die at random from the dice bag and roll it2. You may resolve the rolled result and then return the die to the bag or reroll the die one time and resolve that result, then return the die back to the dice bag. If you choose not to use the die, you can return it to the dice bag. You may also reserve it by placing it on your card without changing the face rolled. If you already have a reserved die, it will replace this reserved die, which goes back into the bag. You may only have one die reserved at a time.

so a strict reading of this implies that you can reroll a die that you reserved on a previous turn. Is that correct?

And on the same line, according to the rules that rathstar reproduced here: If you reroll your die, are you forced to use/reserve the second result you get, or can you still return it to the bag without using it?